三轴应力下卵石混凝土力学性能与本构关系

为研究卵石混凝土的三轴受压力学性能,进行了27个卵石混凝土试件的常规三轴试验,观察了试件的破坏形态,获取了其应力-应变全过程曲线及特征点参数,深入分析了围压对卵石混凝土力学性能的影响.结果 表明:随着围压的增大,卵石混凝土试件破坏形态先由轴向劈裂破坏转变为斜向剪切破坏,再转变为横向剪切破坏;围压越大,峰值应力、峰值应变...     

基于IEC 61850的变电站网络安全分析

基于IEC 61850的数字变电站自动化系统是一个基于网络的开放式系统。随着开放性的增加,变电站的网络安全问题越来越突出。IEC 61850标准明文规范了变电站的网络通信协议,但未提供相关的安全规范。文章分析了基于IEC 61850的变电站网络系统安全体系,总结了IEC 62351的相关应用,并指出了IEC 62351今后的改进方向。     

步进扫描投影光刻机同步机制研究

分析了步进扫描投影光刻机的同步运动过程,将各个分系统分为同步主系统和同步从系统,采用串行同步总线实现了同步主系统的状态发布;分析了分系统与自身数据采集系统的同步通信,采用高速串行传输链路实现了分系统与远程数据采集系统的数据采集与通信;搭建了同步实验平台,对步进扫描投影光刻机的同步机制进行了验证。实验证明该平台稳定可靠,满足系统同步性能要求和工程要求。     

VxWorks在糖厂pH值监控系统中的应用

介绍了嵌入式操作系统VxWorks在糖厂pH值监控系统中的应用.糖厂pH值监控系统包括pH值信号采集、液晶显示、触摸屏、Modbm通信协议、步进电机驱动与控制等功能.借助于VxWorks操作系统的强大的任务调度功能.成功解决了监控系统的实时性和多重任务调度之间的冲突,提高了糖厂pH值监控系统的性能.     

乙醇柴油混合燃料助溶剂的试验研究

选用正丁醇、正庚醇和正癸醇作为乙醇-柴油混合燃料助溶剂(混合燃料的体积比为助溶剂:乙醇:柴油=5:20:75)进行相溶性试验,并通过台架试验对比了添加不同助溶剂的混合燃料对柴油机性能及排放的影响.试验结果表明:随着正构醇分子量增加和环境温度上升,混合燃料相溶稳定性增加,燃油经济性变好;HC和NOx排放随助溶剂分子量增加和发动机转速降低而上升.在1 500～2 200 r/min时,zH5E20D75的烟度最低.其余转速下则以ZD5E20D75为最低.     

模拟企业生产的现代机械制造大实验平台构建的研究

针对在知识经济和全球市场经济的形式下,剧烈竞争的焦点将聚集于创新人才的竞争,探讨了机械制造业创新型人才的培养途径;设计了适合机械制造业创新人才培养模式的实验独立设计课,构建出模拟现代企业生产的现代机械制造大实验平台.     

富水土壤源热泵供冷采暖机组运行特性研究

介绍了作者自主设计实施的土壤换热器与冷却塔并联的耦合型地源热泵空调系统,运用单因素方法,研究了冬夏两季热泵机组的运行特性;研究结果表明:夏热冬暖地区,本实验系统夏季采用热泵机组匹配土壤源释热的制冷效果一般,制冷工况热泵机组能效比约3.66,系统能效比约2.7;冬季采用热泵机组向建筑物供暖效果较佳,系统能效比达3.4以上.     

Nanocrystalline LaMnO3 preparation and kinetics of crystallization process

Precursor of nanocrystalline LaMnO₃ was synthesized by solid-state reaction at low heat using La(NO₃)₃·6H₂O, MnSO₄·H₂O, and Na₂CO₃·10H₂O as raw materials. XRD analysis showed that precursor was a mixture containing orthorhombic La₂(CO₃)₃·8H₂O and rhombohedral MnCO₃. When the precursor was calcined at 800 ^°C for 2 h, pure phase LaMnO₃ with rhombohedral structure was obtained. Magnetic characterization indicated that rhombohedral LaMnO₃ behaved weak magnetic properties. The thermal process of the precursor experienced four steps, which involved the dehydration of crystallization water at first, and then decomposition of manganese carbonate into MnO₂, and decomposition of La₂(CO₃)₃ and MnO₂ together into La₂O₂CO₃ and Mn₂O₃, and lastly reaction of monoclinic La₂O₂CO₃ with Mn₂O₃ and formation of rhombohedral LaMnO₃. Based on the Kissinger equation, the value of the activation energy associated with the formation of rhombohedral LaMnO₃ was determined to be 260 kJ mol^?1. The value of the Avrami exponent, n, was equal to 1.68, which suggested that crystallization process of LaMnO₃ was the random nucleation and growth of nuclei reaction.     

Effects of Bi excess on the structure and electrical properties of high-temperature BiFeO3–BaTiO3 piezoelectric ceramics

BiFeO₃–BTiO₃(BF–BT) ceramics as a promising candidate for lead-free high-temperature piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric properties. Excess Bi was added to compensate for the evaporation of Bi³⁺ ions during sintering and this addition was found to be effective in improving the piezoelectric properties of BF–BT ceramics. The microstructure, dielectric and piezoelectric properties of excess Bi doped BF–BT ceramics were investigated. Maximum piezoelectric constant d ₃₃ = 142 pC/N and k _p = 0.302 were obtained with 0.04 Bi doping. At the same time, an enhanced Curie temperature T _c, 452 °C, was obtained. The combination of improved piezoelectric properties and increased T _c makes these ceramics suitable for elevated temperature piezoelectric devices.     

Lead-free (Li, Na, K)(Nb, Sb)O3 piezoelectric ceramics: effect of Bi(Ni0.5Ti0.5)O3 modification and sintering temperature on microstructure and electrical properties

Lead-free (1 ? x)(K_0.475Na_0.475Li_0.05)(Nb_0.95Sb_0.05)O₃–xBi(Ni_0.5Ti_0.5)O₃ [(1 ? x)KNNL–xBNiT] piezoelectric ceramics were prepared by conventional solid-state sintering. The effect of BNiT addition and sintering temperature on phase structure, microstructure, and dielectric and piezoelectric properties of (1 ? x)KNNL–xBNiT ceramics was investigated. The results reveal that the addition of small amounts of BNiT causes significant changes in microstructures, crystalline structures, and dielectric and piezoelectric properties. The T _c values and dielectric constant at T _c of (1 ? x)KNNL–xBNiT ceramics are increased obviously with 0.2 % BNiT addition and decreased with further increasing BNiT content. Enhanced piezoelectric properties are obtained for the sample with x = 0.4 % and synthesized at optimal temperature of 1100 °C, in which d ₃₃ and k _p are 253 pC/N and 0.52, respectively. These results show that (1 ? x)KNNL–xBNiT ceramics are promising lead-free piezoelectric materials.